1. Field of the Invention
The invention pertains to an apparatus and a method for using it which makes it easy and affordable for the motorist to balance and adjust the air pressure of all four tires on individual vehicles rapidly and simultaneously, thereby providing a greater degree of safety resulting from the more even traction of all of the tires, while also providing a safety to prevent accidental over-inflation which could damage the tires and the apparatus.
2. Description of the Prior Art
The importance of properly inflating tires has been recognized in the prior art, but most of the effort has been directed toward the tires of commercial and industrial vehicles which are inevitably inflated to a much higher pressure than individual vehicles. Thus, attempts have been made to assure that the tires of large commercial and industrial vehicles retain a near-constant air pressure through an elaborate system of sensors, compressors, valves and hoses which increase the pressure in the tires or reduce it if the pressure is excessive. Some of these systems are "on board" and quite complex. Yet little has been done to present a simple, inexpensive and nearly fool-proof way for the owner and/or driver of an individual vehicle to equalize the tire pressure in all four tires on the vehicle. Even when a service station is at hand, the standard air pressure supply system available there makes it extremely difficult for the driver to equalize the pressure in all four tires on an individual vehicle either by increasing or decreasing it in each tire separately. The difficulty in balancing the pressure in the tires on an individual vehicle stems from a number of factors. Thus, in a service station, the gauge that is attached to the hose on the air pressure supply pump is frequently inadequately calibrated to read with accuracy the air pressure that is delivered. Repeated use may have damaged or contaminated the gauge so that it no longer reads the pressure that is delivered, even if it was originally calibrated to do so. Not uncommonly, the gauge will have such a large pressure-reading capacity that small variations in pressure will be difficult to read on the scale. Such gauges may have errors in pressure readings alone of as much as three percent of full scale. Since service stations also service large trucks and their high-pressure tires, the pressure gauges connected to their air pressure supply pumps will have a scale of two hundred psi, ie., two hundred pounds per square inch capacity or even more. If a three percent error exists, it could readily produce an error of as much as six psi in the reading, a very significant twenty-percent error for air pressure in the tires of individual vehicles which normally have tire pressures under thirty psi. Even if a more accurate manual tire gauge is used to determine the pressure in the tires, it is still extremely difficult to inflate all tires accurately to the same desired pressure. Frequently, poor lighting will contribute to that error. As a result, even if care is taken in an effort to inflate all the tires to the same pressure, there may still be differences of several pounds per square inch of pressure among the four tires on the individual vehicle.
It is also well known that an imbalance in air pressure among a set of tires on an individual vehicle can make driving hazardous, especially in periods of inclement weather when the roads are wet or icy. There is nothing currently available to the motorist, either at the service station or in the individual vehicle, that would permit him to inflate all of the tires of his individual vehicle accurately and safely to the same pressure. Yet his safety depends to a large degree on the condition of his tires and tire traction is a significant part of individual vehicle safety. Tire traction is directly related to the tire surface that is in contact with the road as well as to the condition of the road and its surface. A tire with higher air pressure will have less surface in contact with the road and, conversely, a tire with lower air pressure will have more surface in contact with the road. As a result, when the front tires have not been inflated evenly to the same pressure, there can be significant differences in traction between them, with a tendency for the individual vehicle to veer to one side. If the individual vehicle is traveling on a wet or icy road, an imbalance of pressure in the front tires is greatly magnified and can easily cause accidents. Similarly, dangerous conditions exist when the individual vehicle is being accelerated with either the front or the rear tires, or when the brakes are applied to the front or the rear tires when there is an imbalance of pressure in them. Again, this situation is made considerably more dangerous on a wet or icy road.
Consequently, there has existed a need for a better and faster way of balancing the pressures in tires of individual vehicles so that they are as evenly matched as possible. McAnally et al, U.S. Pat. No. 4,872,492 control the amount of pressure provided to individual pneumatic tires, but present difficulty in providing precise equalization of pressure in multi-tire application. Keys, U.S. Pat. No. 4,883,107, provides a dual valve stem which either contains an adapter or to which an adapter is attached; the tire is inflated to a higher pressure than needed and then, upon removal of the air chuck, the pressure in the tires automatically adjusts to a lower pressure through a system of counterbalanced springs. However, while at first sight this appears to be a good idea, there are problems with this patent. Thus, there are the definite dangers of contamination of the pressure-reduction valve, with a loss of air and the inaccuracies that would result therefrom. Besides, the adjustment device would have to be inherently accurate. Springs are notorious for binding and setting. There is nothing within the patent to indicate that an attempt was made to accurately measure the air pressures obtained in actual repeated tire pressure adjustments, i.e., to show that it does what it is supposed to do. For this specific design, it would appear that there could be a wide variation in tire pressures during the use of this device from one tire air-valve to another. Another objection would be the need to keep the device attached to the tire air-valve in light of the increase in torque that would be exerted on the tire air-valve by the additional length and weight of the dual valve stem with the adapter, coupled with the high probability of damage resulting from contamination, transportation/vibration and the possible contact the tire would make with the curb. Da Silva, U.S. Pat. No. 4,875,509 shows a device for simultaneously filling and equalizing the pressure in dual tires, but it is not portable. Moffett, U.S. Pat. No. 5,158,122 designs a portable device for use with dual pneumatic tires in which he patents a high-pressure locking tire chuck valve to secure air supplying hoses to dual pneumatic tire valves. This locking tire chuck valve was needed in his design because of the fact that the pressures in dual pneumatic truck tires may be as high as two hundred psi, i.e., pounds per square inch. But it is not needed here where individual vehicles have much lower tire pressures, i.e., in the twenty-four to twenty-eight psi region. There are other reasons for not using this valve here. Thus, this locking tire chuck valve is complex, not commercially available, and it would be far too costly to produce for use with equipment that would require four such valves for each item produced, as is the case here, making its use here economically undesirable. Moffett also provides an air-bleed valve to reduce manually the pressure in the dual pneumatic tires. This would be superfluous if a tire air-valve fulfills this function as it does here. Also, none of the approaches provide a safety device to prevent accidental over-inflation of the tires.
This invention attempts to overcome the problems and limitations of prior inventions so as to inflate all four tires on individual vehicles simply, safely, economically and simultaneously to the same pressure. It does not do so by relying upon the mechanical qualities of spring-loaded valves since these are unreliable and inaccurate, nor does it resort to the use of expensive components that would make the price excessive for the average motorist.
Instead, the invention relies upon the implementation of a scientifically known principle in a novel way that assures the equalization of the pressures in all four tires on an individual vehicle, and keeps the price down through the use of a low-cost, commercially available connector for attaching to the tire air-valves on all four tires of an individual vehicle. Air may then be added either by a foot-pressure air-pump or by an electrically-powered air-pump, the latter usually being powered from the cigarette lighter outlet of the individual vehicle. But, as was discovered during the use of these low-cost connectors, they do not possess an automated on/off capability when they are attached or detached to tire air-valves.
Thus, when these were tested for use with this invention, it was found that there was considerable air loss during the time when all the connectors were being detached from the four tire air-valves of the individual vehicle, with the greatest air loss occurring when the last tire was being disconnected. This could not be tolerated. A conventional hand-operated shut-off switch was added initially, but was eliminated when it was found that this would complicate the operation of the apparatus by requiring the motorist to turn it on and off repeatedly, thereby making the apparatus much less desirable. Consequently, it was determined that a simple, low-cost, automatic on/off capability (valve) was needed, one that would turn on and off as each connector was attached to a tire air-valve and then detached. Such a valve was designed specifically for this apparatus, with the objectives being low price, reliability and compatibility. It is attached by a clamp to the connector so that it is oriented in such a way that, at the moment of attachment to the tire air-valve, the connector will turn on the tire air-valve and then turn it off at the moment of detachment from the tire air-valve. The connector selected for use in this invention is used in high volume in many air-pumps, making it low in cost and commercially available. It is composed of a cylindrical body and a handle which, in the open position, protrudes in line with the cylindrical body, and wherein a piston located within the cylindrical body is locked in a downward position by pivoting the connector handle down into a ninety-degree position. The piston rests upon a rubber tube, confined top, bottom and outer diameter, within that cylindrical body, taking up about half of the lower open end of the cylindrical body used for attaching the tire air-valve. The rubber tube presses against the piston and prevents it from sliding down within the cylindrical body. When the connector is placed over the tire air-valve, the rubber tube within the connector fits loosely over the threaded portion of the tire air-valve. In order to fit the connector tightly to the tire air-valve, the handle on top of the connector is pivoted down into a ninety-degree position. This action depresses and advances both the piston and a centrally located, small-diameter rod attached to its end. As the piston advances, it compresses the rubber tube which, being confined top, bottom and outer diameter within the connector, can move in only one direction . . . curving inward . . . thereby taking up the space around the threaded portion of the tire air-valve and forming an air-tight connection with it, strong enough to resist internal air pressures of 50 psi. Simultaneously, the forward movement of the small-diameter rod centrally located on the piston causes it to impinge on the stem of the tire air-valve, depressing it and forcing the tire air-valve to open. The pivoting of the handle of the connector to the ninety-degree position, parallel with the cylindrical body, depresses the spring-loaded piston of the shut-off valve into the open position.
When all of the connections with the four tire air-valves have been made, air circulates to all the tires through a central air reservoir (composed for the sake of compactness of a hollow rectangular container with a tire air-valve located on one end), and the pressure then equalizes within the tires and the apparatus. The pressure within the tires can now be read on an air pressure gauge with a scale of fifty to one hundred psi, calibrated to be within one percent of full scale readings, and located on the side of the container opposite to the four outlets. Air pressure can be increased by supplying air from an air pump to the tire air-valve located at one end of the hollow rectangular container, or excess air can be released from it by depressing the valve stem until the desired pressure is read on the air pressure gauge. When the proper pressure reading has been obtained, the connectors are detached, one after another, from the threaded portion of each tire air-valve. This closes both the tire air-valves and the shut-off valves, while retaining the pressure within the tires. The tire air-valve caps are then replaced.
Since the possibility exists that, during the pumping of air into the apparatus, the air-pump may be left unattended and excessive pressure will be pumped into the tires, possibly resulting in damage to the tires and the apparatus, a safety air pressure-relief valve set to open at about thirty-five psi was incorporated within the apparatus and topped off with a whistle that allows the excess air to escape through it, making an audible whistling sound and thereby notifying the motorist that the safety air pressure-relief valve has gone off and that the air-pump should be disconnected.